In present-day methods of diagnosing technical equipment, the detection of existing faults and damage occurring in the early phase of the use of equipment or its individual parts and their accurate location are of paramount importance, and the sooner it can be done the greater the importance of the method. The diagnosing of the condition of equipment and especially the detection and automatic identification of defects in rotating electric machines and their parts makes use of methods based on measuring electric or mechanical signals, their processing as well as the analysis and interpretation of the results of the measurements.
The nowadays applied methods of monitoring bearings during operation consist in comparing the measured and digitally processed results with data obtained for bearings which operate in proper conditions and which are not in danger of any failure. In most cases such comparison is done by an expert trained for this purpose.
The most frequently used method for early determination of defects in bearings consists in the examination of shock pulses combined with the examination of vibrations in the tested parts of the bearing. Then, such shapes of the pulses are selected from the measured data for further analysis which suggest the possibility of the presence of a defect. Computerised methods of data analysis allow to detect faults early and to determine the place of their occurrence, their types and the degree of damage.
A method and a device for checking the condition of a rolling bearing is known from the patent description U.S. Pat. No. 5,477,730. The method consists in detecting the primary signals of vibrations emitted by the bearing, demodulation of these signals to output signals after demodulation, converting the output signals from analogue signals to digital output signals, filtering noise out of these signals by means of a digital filtration technology selected from many known technologies, and outputting the digital signals to an output device. In another variant of the invention, instead of the demodulation of primary signals, band-pass filtration within a range from 2000 to 15,000 Hertz is used, and the signals after this filtration are subjected to transformations as described earlier. In still another variant of the invention the primary vibration signals emitted by the bearing are converted from analogue to digital, whereupon noise is filtered off the signals using a digital filtration technology selected from many known technologies, which includes the action of separation of noise signals from the digital output signals, and then digital signals are introduced to the output device.
A method for evaluating the condition of the elements of a bearing is known from patent application WO 00/04361. This method employs the measurements of bearing element vibrations by generating an analogue acceleration signal, converting this signal into digital data, sampling the digital signal to locate its components coming from the bearing defect. The method is characterized in that the influence of any unwanted, deterministic signal components is removed from the digital acceleration signal by means of filtering so as to obtain a signal consisting essentially of white noise proportional to overall smoothness of the microstructure of the bearing surface and shock pulse. The following signal characteristic parameters that are sensitive to the bearing defects are selected: sharp vibration pulses or shock pulses, peak-to-peak amplitude a mean value proportional to the mean amplitude without shock pulses a peak content of the signal. Detection of narrow-band shock pulses in regular intervals is done using a known method, so called autocorrelation of the envelope signal estimation.